More specifically, it relates to an electrical power supply system of the continuously controlled DC-voltage type. Such system is designed to supply power to various types of equipment that consume electrical energy with a voltage that is constant, regardless of the level of this consumption and the source of energy supplied.
As it is known, and in reference to FIG. 1, such continuously controlled voltage power supply includes the following elements:                a main power bus 11, which is intended to be connected to an equipment set 10 consuming electrical energy;        a plurality of solar generator sections 1, which are connected to the main power bus 11;        a battery unit 2, which has an output terminal B;        a plurality of battery discharge regulator modules, referred to as BDR for “battery discharge regulator” and referenced 3, which are each connected between the output point B of the battery unit and the main power bus 11; and        an error amplifier, which is suitable for producing at least one signal for controlling the current which is to be transmitted to the main power bus 11 in order to maintain the electric potential thereof constant.        
The error amplifier may be of the proportional-integral regulator type. It is referred to as MEA for “main error amplifier” and referenced 4. The electric potential of the main power bus 11 is denoted by VBUS.
Thus, the electrical power supply system includes two power sources: the solar generator sections 1, and the battery unit 2. The number of solar generator sections 1, as well as the capacity of the battery unit 2, is set according to an average electricity consumption of the equipment set 10. Each solar generator section 1 includes a DC-current generating line 1g and a switch 1s. The switch 1s is suitable for directing an electric current that is produced by the line 1g to the main power bus 11, or for inhibiting an output of this current to the bus 11. In so-called daytime operation, i.e. when the solar generator sections 1 are illuminated by the sun, they produce an electric current that is transmitted by the main power bus 11 to the equipment set 10. Possibly, if this current is insufficient with respect to the consumption of the equipment set 10, it is complemented by a discharge current from the battery unit 2, denoted by IDIS in FIG. 1. In nighttime operation, i.e. when the solar generator sections 1 are not producing any current, the equipment set 10 is powered only by the battery unit 2.
As an example, the constant potential VBUS of the main power bus 11 may be equal to 50 V (volts), and the average power consumption of the equipment set 10 may vary between 5 or 10 kW (kilowatt).
As it is known, each BDR module 3 may include a voltage converter that makes it possible to transfer an amount of current from an input of the module having an electric input potential to an output of the module having an electric output potential. This current amount is determined by a control signal that is transmitted to a control input of the module. In the system of FIG. 1, the input of each BDR module 3 is connected to the output point B and its output is connected to the main power bus 11. The input potential of the modules 3 is therefore that of the output point B of the battery unit 2, and the output potential of the modules 3 is VBUS. The current that is transmitted by the BDR modules 3 to the main power bus 11 is then IDIS×VB/VBUS.
In daytime operation, the two electrical power supply modes, from the solar generator sections 1 alone or from both the latter and the battery unit 2, are controlled by the amplifier 4. To this end, the amplifier 4 compares the actual electric potential VBUS of the main power bus 11 to a fixed target value, which is the desired power supply potential.
When the solar generator sections 1 alone would supply a current that is too important for the consumption of the equipment set 10, the error amplifier 4 reduces the average number of solar generator sections 1, which are electrically connected to the main power bus 11, in order to prevent the potential VBUS thereof from exceeding the desired value. To this end, the amplifier 4 is connected to the control input of the switch 1s of each solar generator section 1, so that an average current that is transmitted by these sections can be adjusted according to the control signal produced by the amplifier. Practically, the adjustment is achieved by intermittently controlling the transmission, to the main power bus 11, of the current of some of the sections 1. The regulation of the potential VBUS then results from a period ratio of transmission/inhibition times. The amplifier 4 simultaneously controls a blockage of the battery discharge regulator modules 3, so that no current is supplied by the battery unit 2 (IDIS=0).
When the current supplied by solar generator sections 1 is insufficient with respect to the consumption of the equipment set 10, the error amplifier 4 controls a transmission, to the main power bus 11 of the unit, of the current that is produced by the sections 1, and simultaneously activates the BDR modules 3. The latter then adjust the discharge current IDIS of the battery unit 2 so as to supply power to the equipment set 10 by keeping the electrical potential VBUS of the bus 11 constant. To this end, the amplifier 4 is also connected to the control input of each BDR module 3, so that the discharge current of the battery unit 2 is adjusted according to the control signal produced by the amplifier.
These two modes of adjusting the current supplied to the main power bus 11, by controlling in a variable manner the switches 1s of the solar generator sections or the BDR modules 3, may be distinguished, for example in a known manner, by the sign of the control signal which is produced by the amplifier 4.
It is understood that a capacitor connected between the main power bus 11 and a reference terminal of the system, and which is not shown, may be used to reduce residual variations of the potential VBUS.
Finally, to recharge the battery unit 2, the system also includes at least one battery charge regulator module 7, denoted by BCR for “battery charge regulator”. This module 7 is electrically connected between the main power bus 11 and the output point B of the battery unit 2. It is activated by the amplifier 4 when the solar generator sections 1 can produce a current which is higher than the consumption of the equipment set 10. The module 7 then controls a charge current, denoted by ICH, which circulates from the bus 11, through said module 7, to the battery unit 2. This charge current is adjusted according to the charge level of the battery unit 2, according to a charge characteristic that is provided by the manufacturer of this battery unit.
However, the use of such a battery charge regulator module has the following disadvantages:                it involves increasing the weight of the satellite, which is particularly detrimental in terms of the initial costs of this latter;        it is expensive, in particular because it involves a power component, by contrast with control components; and        as a voltage converter, it produces heat which must be evacuated appropriately in the satellite.        
To avoid these disadvantages of battery charge regulator modules, document EP 1 073 176, which corresponds to U.S. Pat. No. 6,157,161, discloses an electrical power supply system for a satellite with continuously controlled DC-voltage, which is devoid of BCR module. In this system, certain solar generator sections are connected to the main power bus of the equipment set, and to the input of the battery unit by means of controlled switches. When one of these switches is open, so that the corresponding solar generator section is no longer connected directly to the battery unit, this solar generator section can participate in supplying power to the equipment set in the usual manner, as described above. When one of the controlled switches is closed, so as to electrically connect the corresponding solar generator section to the battery unit, the latter is recharged directly, without the charge current produced by the section passing through the main power bus. However, in such a power supply system, the charge current of the battery unit can be adjusted only by varying the number of solar generator sections that are temporarily connected to the battery unit. For this reason, this charge current cannot be finely adjusted with respect to the state of charge of the battery unit that is already achieved. This maladjustment of the charge current can reduce the lifetime of the battery unit, and therefore reduce the operating life of a satellite equipped with this power supply system.